Auxiliary air inlet door and duct coupling for jet aircraft air inlet ducts



April 9, 1957 H.

AUXILIARY AR IN E. MICHAEL LET DOOR AND DUCT COUPLING FOR JET AIRCRAFTAIR INLET DUCTS f Filed 0G13. 5, 1955 2 Sheets-Sheet l April 9, 1957AUXILIARY AIR INLET DOOR AND DUCT COUPLING 1 H. E. MICHAEL 2788,184

A RoR JET AIRCRAFT AIR INLET DUcTs Filed Oct. 5, 1953 2 Sheets-Sheet 2United States Patent O l AUXILIARY AIR INLET DUUR AND DUCT COU- PLINGFDR JET AIRCRAFT AIR INLET DUCTS Harold E. Michael, Hawthorne, Calif.,assigner to N orthrop Aircraft, Inc., Hawthorne, Calif., a corporationof California Application October 5, 1953, Serial No. 383,951

6 Claims. (Cl. 244-53) The present invention relates to air inlets forgaseous combustion turbines installed in airplanes, and moreparticularly to a means for decreasing the inlet pressure loss in airinlets for such engines during airplane take-off. The present inventionis an improvement of the device shown, described and claimed in anapplication for U. S. patent, Serial No. 123,466, led October 25, 1949,now Patent No. 2,699,906.

In high speed airplanes utilizing engines of the gaseous combustiontype, particularly those airplanes powered by gas turbines taking theircompressor inlet air from the side of the fuselage, or the leading edgeof a wing, the air inlets are relatively small, and usually have sharp,thin duct lips. Such inlet construction is highly desirable duringcruising and high speed iiight because of the consequent decreasedfrontal area and drag, and increased critical Mach number. At standstillor take-off, however, the performance of the gas turbines is impairedbecause of high unit airflow per unit inlet area, with the benefit oflittle or no ram pressure. In view of the desirable qualities of smallengine air inlets and sharp, thin duct lips, it was found beneficial toprovide a means of improving take-off performance which did not requireincreasing the normal inlet area or a change in duct lip contour.

In addition, jet engines are usually quite long and extend well ahead ofthe thrust connections to the airplane. This extension is usually longenough so that the compressor end of the engine moves longitudinallyforwardly a substantial distance when brought up to maximum temperaturefrom a cold condition. This movement can be accommodated by providing agap between the forward end of the engine and the inboard end of the ramair inlet duct, this gap usually bridged by some resilient materialpermitting free longitudinal expansion and contraction of the enginewith respect to the opposed outlet of the ram air inlet duct. However, Ihave found that this gap, using special closures in accordance with thepresent invention, can be eiciently utilized for the admission ofauxiliary air before ram pressure develops in the air inlet duct duringflight.

Among the objects of the present invention are:

To provide a novel means for reducing pressure loss in inlets for gasturbine engines used in airplanes, at low airplane speeds.

To provide an additional inlet area for gas turbine engine inlets inairplanes to reduce pressure losses on airplane take-E.

To provide an automatic means of regulating air intake area for gasturbine engines during airplane take-off.

To provide a means in an airplane for utilizing a gap between theforward end of a jet engine and the rear end of an air inlet duct toadmit auxiliary air which at the same time provides for enginecontraction and elongation.

To provide means for closing the gap required to accommodate jet engineexpansion and elongation when installed in an airplane, said closuremeans being capable 2,788,184 Patented Apr. 9, 1957 ICC of use as anauxiliary air inlet in any engine position.

And to provide a novel means connecting the forward end of a jet enginewith the -rear end of a ram air inlet duct to said engine in anairplane.

In most high speed airplanes equipped with gas turbine engines, anegative pressure is created inside the engine air inlet ducts due tothe pressure losses in the inlet, when the airplane is standing still ormoving slowly. This condition creates a loss in take-oit power, whichloss can be greatly reduced by admitting auxiliary air to the compressorthrough an auxiliary air inlet adjacent the compressor inlet, under thecontrol of doors operated by the differential pressure existing betweenthe compresser inlet and the atmosphere. The doors open when a negativepressure exists in the ram air inlet duct, and close when a positivepressure is built up in the air inlet duct due to ram developed in fullflight.

The present invention utilizes a construction providing a gap entirelyaround the compressor inlet between a member on that inlet and a memberon the opposed inboard end of the ram air inlet duct of the airplane.The compressor end of the engine and the opposed inboard end of the ramair inlet duct are so spaced that a substantial gap will always existtherebetween at the maximum longitudinal expansion of the engine.Peripheral closures are then provided for the gap, hinged on one memberto swing inwardly and slidably engageable with the other member, so thatthe engine is free to expand and contract longitudinally irrespective ofthe position of the peripheral gap closures.

Auxiliary air is made available for passage through the gap when anegative pressure is developed at the compressor inlet, by providingdoors in the outer skin of the airplane or engine nacelle adjacent thegap, and then sealing the space between the gap and the doors so thatthe doors, which are preferably spring loaded to remain normally closed,are also opened by the negative pressure developed in the space. Thus aneiiicient auxiliary air inlet is provided all around the compressorinlet, with perfect freedom of longitudinal movement of that inlet undervarious engine operating conditions.

The invention can be better understood by reference to the followingdescription of a preferred embodiment of the invention as shown in thedrawings in which:

Figure l is a perspective view from one side of part of an airplaneutilizing said preferred embodiment, a part of an engine nacelle beingin a cutaway sectional View for additional clarity.

Figure 2 is a longitudinal sectional view of the ram air inlet duct andfore portion of a jet engine as mounted in the nacelle shown in Figurel.

Figure 3 is an enlarged detailed sectional View of a gap closure.

Figure 4 is a closure.

Figure 5 is a skin inlet doors.

Figure 6 is a cross sectional view taken as indicated by the line 6-6 inFigure 5.

Referring first to Figure l, an airplane 1 is driven by two jet engines,one of which 2 is shown mounted in a lateral engine nacelle 3. A ram airinlet 4 is provided at the forward end of the nacelle 3, leading into aram air inlet duct 5 directed `rearwardly and terminating at aperipheral inboard end flange 6, best shown in Figures 3 and 4.

The jet engine 2 is mounted on a thrust bracket (not shown) rearwardlyof engine compressor section 7 of the engine 2, the engine beingpositioned horizontally by the use of a hinged ball and socket bracket81 attached beperspective view from outside, of a gap perspective viewfrom the inside, of the The forward end of the engine is therefore freeto move longitudinally as the engine changes temperature in operation.

The compressor inlet i@ is provided with a forwardly and outwardlyextending flange 11 this ilange having an inner peripheral closurebearing surface 12 (Figure 3).

Compressor inlet liange 1i is spaced away from inboard end iiange 6 ofthe ram air inlet duct 5 to provide a gap G between said flanges, thisgap for example, when a 5000 lb. static thrust jet engine is installed,being preferaoly on the order of several inches at all times.

At intervals around the rear face a of the inboard end ange 6, arepositioned pairs of hinge brackets 14 extending rearwardly. Each pair ofhinge brackets has hinged thereto a closure bracket 15 attached to aclosure i6. Closures 16 are cylindrical segments, and each is providedwith aside oiset 17 overlapping the adjacent edge 18 of the nextclosure, as best shown in Figure 4.

The closures are longer than the extent of the gap, and the rear edges2d of the closures ride on the closure bearing surface 12 of thecompressor inlet 1d at all compressor inlet positions. Consequently, theclosures can only open inwardly as indicated by the broken line L inFigure 3. Bearing surface 12 is made long enough to provide for theentire possible expansion distance Ex, as also shown in Figure 3. Asuicient number of closures are provided to pass around and completelyclose gap G.

The outer slin 21 of the airplane nacelle is -adjacent the gap G, and isspaced therefrom to form an auxiliary air space 22 this space beingclosed in front by lip 23 of the ram air inlet duct 5 and at the rear bya iirewall 24, the latter peripherally contacting the engine 2 at asliding seal 25 as shown in Figure 2. Thus negative pressure at thecompressor inlet 10 pumps out space 22 to substantially the samenegative pressure as at the inlet.

Auxiliary air is admitted to space 22 through a plurality of auxiliaryair doors 30, spring loaded to remain normally closed, flush with theremainder of the nacelle skin.

These doors can open under a negative pressure in space 22 to admit airthereto. It has not been found necessary in practice to spring loadclosures 16 to normally stay in closed position, although there is noobjection to such positioning, as development of a negative pressure atthe compressor air inlet as the engine starts immediately causes theclosures to open.

As the closures 16 open, space 22 is pumped out, and doors 30 open, thusproviding adequate air for the cornpressor when the airplane isstanding, or at a speed where substantial ram pressure is absent fromthe ram air inlet duct 5.

As the airplane increases speed, as in a take-olf, ram pressure developsin the compressor inlet duct 5, reversing the air flow through closures16, closing them. Negative pressure disappears from the space 22,thereby permitting doors 30 to close in accordance with the spring urgeapplied thereto. Thus in iiight all air goes to the engine through theram air inlet duct 5.

Due to the substantial overlap of the closures 16 on the bearing surface12 of the compressor inlet flange 11, front end of the engine is free tomove longitudinally, even though the |closures 16 lare closed, as therear edges of the latter are free to slide over the bearing surface 12,

Thus the closures 16 not only act as auxiliary air inlets prior to andduring take-oli, but also act as engine to inlet duct seals in ilight.

While in order to comply with the statute, the invention has beendescribed -in language more or less specific as to structural features,it is to be understood that the invention is not limited to the specificfeatures shown, but that the means and construction herein disclosedcomprises a preferred form of putting the invention` into effect, andthe' invention is therefore claimed in any of its forms or modificationswithin the legitimate and valid scope of the appended claims.

What is claimed is:

l. In an airplane driven by a gas turbine engine comprising a compressorand having a compressor air inlet opening at one end of said engine; anair duct in said airplane having an outlet opening opposed to andadjacent said compressor air inlet opening, means for supporting saidengine to permit axial thermal expansion and contraction from saidsupporting means toward said inlet opening thereof to change therelative position of said compressor air inlet opening and said air ductoutlet opening, said engine support being positioned with respect tosaid air duct outlet opening to provide a gap between said air ductoutlet opening and said compressor air inlet opening under all operatingconditions, and segmental closure means hingedly attached around theperiphery of said outlet opening and opening inwardly, said closuremeans when closed slidably contacting the interior rim of saidcompressor air inlet opening to permit expansion and contraction of saidengine in any engine position.

2. in an airplane driven by a gas turbine engine comprising a compressorand having a compressor air inlet opening at one end of said engine; anair duct in said airplane having an outlet opening opposed to andadjacent said compressor air inlet opening, means for supporting saidengine to permit axial thermal expansion and contraction from saidsupporting means toward said inlet opening thereof to change therelative position of said compressor air inlet opening and said air ductoutlet opening, said engine support being positioned with respect tosaid air duct outlet opening to provide a gap between said air ductoutlet opening and said compressor air inlet opening under all operatingconditions, and ysegmental `closure means hingedly attached around theentire periphery of said outlet opening and opening inwardly, saidclosure means when closed slidably contacting the interior rim of saidcompressor air inlet opening to permit expansion and contraction of saidengine in any engine position.

3. A gas turbine engine comprising a compressor and having a compressorair inlet opening at one end of said engine, an air inlet duct having anoutlet opening opposed to and adjacent but spaced forward of said1compressor `air inlet opening and completely free therefrom to providea gap between said air inlet duct outlet opening and said compressor airinlet opening, means for connecting the exterior of said gap to aysource of substantially static pressure, and closure means operablesolely by the pressure diiferential on each side of `said gap to openand close said gap, said closure means when yclosed slidably contactingthe rim of said compressor air inlet opening to permit expansion andcontraction of said engine in any position of said closure means.

4. In an airplane driven by a gas turbine engine comprising a compressorand having a compressor air inlet opening at one end of said engine; anair duct in said airplane having an outlet opening opposed to andadjacent said compressor air inlet opening, means for sup porting saidengine to permit axial expansion and contraction from said supportingmeans toward said inlet opening thereof to change the relative positionof said compressor air inlet opening and said air duct outlet opening,said engine support being positioned. with respect to said air ductoutlet opening to provide a gap between said air duct outlet opening andsaid compressor air inlet opening under al1 operating conditions, andsegmental closure means hingedly attached around the periphery of said`outlet opening and opening inwardly, said closure means when closedIslidably contacting the interior rim of said compressor air inletopening to permit expansion and contraction of `said engine when saidclosure means are closed.

5. In an airplane driven by `a gaseousy combustion turbine engine havinga compressor andV a compressor air inlet opening, combustors, turbineand jet exhaust therefrom, the improvement comprising means forsupporting -sa-id engine in 'said airplane with said engine free toexpand longitudinally and forwardly as said engine heats `up inoperation; Ia ram air inlet duct xed to said airplane and having an airoutlet opening opposed to and spaced from 'said compressor air inletopening under all operating conditions, a plurality of segmental`closures hingedly attached to the rim of one of said openings andopening inwardly, and having suicient length to (bridge the gap between'said openings at the minimum forward expansion of said engine, saidclosures having a peripheral extent sufficient to `close ysaid gap whensubjected to ram air pressure in said duet in any position of saidengine, and means for conducting auxiliary air under relatively lowpressure to the outside of said closures, whereby' When a negativepressure exists in said air inlet duct, said doors will open to admitsaid auxiliary air directly into said compressor'.

6. in an airplane driven by a gaseous combustion en* gine of the-compressonturbine type, the compressor of said engine having aforwardly facing compressor air inlet, a main air duct 'having a ram`air inlet yat one end and having at the other end an air outlet opposedto lbut spaced from said compressor air inlet to form a gaptherebetween, gap closure means positioned around said gap and movableto close said gap by the action of and when a substantial ram airpressure is developed in said main air duct during Hight of saidairplane, an auxil- 'iary air inlet in said airplane substantiallycloser to said compressor air inlet than -said ram air inlet and subjectto `substantially no ram yair pressure when `said airplane is in Hight,means Iconducting air from said auxiliary air inlet around said gapyoutside of the closures therefor, and an inlet 4closure for saidauxiliary air inlet, said latter closure being spring loaded to normallyremain closed, `said latter closure being openable solely by negativepressure developed at said compressor inlet through open gap `closuremeans when said engine is running in the absence of substantial ram airpressure in said main air duct.

References Citedfin the file of this patent UNITED STATES PATENTS2,604,278 Johnson July 22, 1952 2,631,796 Williamson Mar. 17, 1953

